The invention relates to a laser machining apparatus for welding and cutting a workpiece by means of a laser beam.
A conventional laser machining apparatus is disclosed in the U.S. Pat. No. 4,698,483 (Japanese laid-open publication No. 62-130778).
FIG. 5 shows a perspective view of a conventional laser machining apparatus for welding and cutting the workpiece. In the figure, the laser robot machining apparatus construction is illustrated with an emphasis on the laser beam path.
The construction and operation of the conventional laser robot apparatus will be hereinafter described.
As shown in FIG. 5, a laser robot 1 is constructed with five axial (J1-J5) multi-articulated arms. A laser oscillator 2 generates a laser beam. A beam transmitting apparatus 3 transmits the laser beam generated in the laser oscillator 2 to a laser robot 1. The beam transmitting apparatus 3 is constructed of bend mirrors (BM1, BM2) which change the beam direction, beam ducts (usually cylindrical pipe) which protect the human body from the laser beam and supporting members (not shown) which support the beam ducts. When a laser beam having linearly polarized light is converted into a beam having circularly polarized light in order permit the cutting of a workpiece, a retarder (linear/circular converter) is used as the bend mirror BM1. Ordinarily, a bend mirror BM2 is supported by a light axis regulator. The light axis regulator regulates the angle of the beam in two axis directions, i.e., the up-down, right-left directions, and aligns the laser beam with the light axis of the beam duct. A window lens 12 is mounted on the path of the laser beam and isolates the working gas sprayed from a nozzle 14 and prevents the working gas from entering into the beam duct of the laser robot (see FIG. 6). In this manner fumes or dust generated from the surface of the workpiece during welding may not enter into the beam duct, into the beam transmitting apparatus and into the outlet of the leaser oscillator.
The operation of the conventional device may be hereinafter described with reference to FIG. 5.
The laser beam radiated from the laser oscillator 2 is introduced into the laser robot 1 through the beam transmitting apparatus 3. The direction of the incident laser beam is changed from a horizontal to a vertical direction by a bend mirror M1 mounted at one end of a swivel axis (the J1 axis) on the base of the laser robot 1. The bend mirror M1 is mounted so that the laser beam is incident into the center of the bend mirror M2 that is fixed at the other end of the J1 swivel axis. The bend mirror M2 also is mounted on the end of J2 axis (under arm axis) so that the laser beam is incident into the center of a bend mirror M3 that is fixed at the other end of the J2 axis. The laser beam that is changed in direction at the bend mirror M3 is then sent to the center of a bend mirror M4.
The bend mirror M4 is mounted at a front direction on the J3 axis (upper arm axis) so that the laser beam is incident onto the center of a bend mirror M5 that is fixed at another-location along the J3 axis. Further, the laser beam that is changed in direction at the bend mirror M5 is sent to the center of a bend mirror M6 that is mounted on the J4 axis (wrist rotation axis) in a work head portion 4.
FIG. 6 shows a detailed figure of the work head portion 4, beginning at the wrist axis J4 of the laser robot 1 in FIG. 5. In FIG. 6, laser beam 11 is transmitted to a bend mirror M6 through the beam duct. The bend mirror M6 is a mirror which changes the direction of the laser beam by 90 degrees. A window lens 12 operates so that the laser beam can pass through it, but the working gas can not pass through it. A metal parabolic mirror 13 collects the transmitted laser beam and directs it toward a focus 15 on a workpiece surface. A nozzle 14 sprays the working gas from its tip into the surface of the workpiece. A gas supplying inlet 18 supplies the working gas into the gas nozzle 14.
The operation of wrist axis portion of the robot machine is described hereinafter. The bend mirror M6 is mounted so that the laser beam is transmitted to the center of the parabolic mirror 13 mounted on the J5 axis (wrist shaking axis). Each of bend mirrors M1 to M6 is able to have its angle changed in two axis directions. In order to direct the laser beam toward the focus point 15, a parabolic mirror is generally used for a welding robot while a lens is used for a cutting robot.
It should be understood that in the present embodiment, a parabolic mirror for collecting the laser beam is used because a welding robot machine is described in the embodiment, but that the lens would be applicable to a cutting robot with an appropriate change as noted above. Regarding the welding robot, the window 12 is mounted between the bend mirror M6 and parabolic mirror 13 so that working gas does not flow backward into the beam duct. Further, the gas inlet 18 is mounted downward of the window 12 and supplies working gas to the workpiece through gas nozzle 14.
The conventional laser robot machine has many limitations.
First, fumes or dust will adhere to the surface of the window lens during a cutting and welding operation. Also, the window lens is heated by the laser beam (heat lens phenomenon). As a result the surface of the lens will shift the position of the focus point 15. Under the worst case it becomes difficult to carry out an accurate and consistent welding or cutting of the workpiece.
In the welding robot, the working gas pressure is controlled to be maintained at a low level so that the working point is thoroughly covered by the working gas. Therefore the fumes and dust generated at the surface of the workpiece enter into the beam duct from the tip of the nozzle 14 and adhere to the parabolic mirror 13 and window lens 12. In this case, the laser beam is distorted and attenuated by the influence of the adhered fumes and dust. Also, the absorption of the laser beam will generate heat in the window lens 12 and cause a partial transformation in it, somewhat like the formation of a cataract in the human eye. The partial transformation works as a lens and changes the route of the laser beam. Therefore the focus of the beam is changed or shifted. In the worst case, the window lens 12 will be melted by the heat generated in the lens. As a result, it is necessary to change the window lens frequently, which is very expensive.
Second, the fumes and dust that adhere onto the lens and mirror will decrease the transmission and reflection rates, thereof respectively, and thus the overall transmission efficiency. For preventing the adhesion of the fumes and dust, an air purge operation is carried out using a washing gas (for example, clean air) in the conventional laser robot machine. However, the air purging equipment is expensive and its operating costs are very high.